Clarkson was on his way to becoming pre-30-goal scoring Clarkson. He tailed off pretty significantly after a big start in 2013.
Kovy's heart wasn't in NJ and the NHL anymore, and judging by his KHL year, he looks like he's declining. I'll always believe he knew he wasn't up to the rigors of an 82-game NHL season anymore. He found somewhere he could play a lot less games, (hopefully) take less physical abuse, and still make a lot of coin.
Parise can clearly still contribute at a Parise-like level, but we all knew that he would in the immediate future. Losing him stung the most, from a pure wish-we-had-him-right-this-second standpoint, but I really don't miss the other two so much.